The invention relates to a method of controlling the percussion power of a percussion device in a pressure fluid operated rock drilling apparatus, wherein pressure fluid is supplied simultaneously to the percussion device and through a pressure reduction means to a feed device and wherein the percussion power is controlled by adjusting the pressure of the pressure fluid supplied to the percussion device.
The invention is also concerned with an arrangement for controlling the percussion power of a percussion device in a pressure fluid operated rock drilling apparatus, comprising a pressure fluid pump, a percussion device and a feed device the supply line of which is connected to a pressure line for the pump, and at least one pressure reduction means connected between the pressure line of the pump and the feed device to reduce the pressure of the pressure fluid to be supplied to the feed device to a value lower than the pressure of the pressure line of the pump.
Percussion pressure in rock drilling apparatuses and their actuating means has been previously adjusted to a certain fixed value and the feed of the drifter has been adjusted by varying the pressure of the feed device in accordance with the kind of the rock to be drilled, which often causes problems.
If the feed pressure is too low with respect to the percussion pressure, the feed rate being lower than required or allowed, the percussion impulse will not be properly transmitted along the drill rod into the rock to be drilled, but causes vibration in the drill rod and the rest of the drilling equipment. The vibration is gradually converted into heat, the greatest temperature rise occurring in the threaded couplings of the drill rods or the like so that these parts in particular are exposed to extra strain. This may cause damage to the drilling equipment, or the drilling equipment may wear more rapidly than normal with resultant shorter service life and higher operating costs. At the same time the penetration rate of the drill into the rock is decreased and more time is required for drilling a hole of a determined length, which further increases the drilling cost. Vibration also subjects all the other mechanical and hydraulic components of the drilling equipment to an extra strain, increasing the need of maintenance and repair in the long run.
The object of the present invention is to provide a method and an arrangement for controlling the drilling process of a rock drilling apparatus, which avoids the above-mentioned difficulties and enables the drilling process to be carried out in the best possible way with regard to the conditions. The method of the invention is characterized in that the pressure fluid is supplied by means of a pressure-controlled volume flow pump, the volume flow of the pump being controlled by means of the pressure occurring between the feed device and the pressure reduction means and the ratio of the pressures of the pressure fluids to be supplied to the percussion device and the feed device, respectively, being adjusted to a substantially constant value by means of a pressure control means connected in series with the feed device.
The basic idea of the invention is that the ratio of the percussion pressure to the feed pressure is kept substantially constant by adjusting the percussion pressure in proportion to the feed pressure so that the power of the percussion impulse depends directly on the level of required feed pressure and by using a pressure-controlled pump the volume flow of which is adjustable on the basis of the feed pressure. When the percussion power is proportional to the volume flow entering the percussion machinery, variation in the feed pressure causes similar variation in the percussion pressure, keeping the percussion pressure and, as a consequence, the percussion power proportional to the feed pressure.
The arrangement of the invention is characterized in that the pump is a pressure-controlled volume flow pump, the pressure fluid line going to the feed device being connected to a control pressure line for the pump between the pressure reduction means and the feed device, the pump comprising at least one pressure control means connected to the supply line of the feed device in series with it to keep the pressure of the pressure fluid to be supplied into the percussion device at a substantially constant ratio relative to the pressure occurring in the supply line of the feed device.
The basic idea of the arrangement of the invention is that the supply line of the feed motor is connected to the control pressure line of the pressure-controlled volume flow control pump, so that the volume flow of the pump is adjusted on the basis of the feed pressure of the feed motor. The supply line further comprises a pressure control means which keeps the ratio of the percussion pressure to the feed pressure substantially constant.
The invention will be described in greater detail in the following drawings, in which